1. Field of the Invention
This invention relates generally to exercise machines, and is particularly concerned with exercise machines of the type which simulate free weight barbell exercise movements.
2. Related Art
Weightlifting machines with weight bars for simulating barbells, also known as Smith machines, have been a fitness club staple for many years. The basic machine has a barbell attached to slide mechanisms which run on vertical guides on opposite sides of a stationary frame. This allows an exerciser to perform exercises with vertical up and down movement, such as squats, bench press exercises, and the like, but does not permit any horizontal movement. The exerciser does not have to worry about balancing the side-to-side or front-to-back movement of an independent, free weight bar. The premise is that this design provides an additional measure of safety and is easy for the neophyte to use.
The first Smith machines had the vertical guides running perpendicular to the floor, which worked well for some exercises such as squats but fought the natural chest-to-chin arcing movement of a bench press. Manufacturers soon started designing Smith machines that placed the vertical guides at a slight (five to seven degrees) angle. These new designs worked better for exercises which involved travel in a slight arc, but not as well for other exercise motions which tended to follow a straight line.
The next evolution came with the advent of composite motion or dual action Smith machines that provided simultaneous horizontal and vertical exercise motion. These designs allowed the exercise bar to follow a natural front-to-back exercise motion but still eliminated the side-to-side balancing worries. They provided a halfway point between the balance and coordination needed to perform free weight exercises and the security of a traditional Smith machine. These designs also provided the ability to perform exercises such as lunges which require greater horizontal movement.
Dual motion weightlifting machines typically have a horizontal exercise bar which is slidably mounted at its opposite ends on two vertical guide bars. Each vertical guide bar in turn is slidably mounted on horizontal guide bars at its upper and lower ends. This allows the exercise bar to move simultaneously in vertical and horizontal directions, so that the exerciser can perform a more natural feeling weightlifting exercise which allows for the natural horizontal movements of the arms while pushing a weight upwards. The weight bearing bar or exercise bar is normally a standard Olympic bar, which may have hooks attached to it on a rotatable sleeve for hooking onto pinning holes on vertical guides so as to hold the bar in a rest position. The usual weight for an Olympic bar is between forty and fifty pounds. By attaching hooks, bearings, and vertical slides, the weight is dramatically increased. In some cases, counterweights are added to help reduce the weight or inertia required to move the bar from a rest position. While this counterbalance offsets the vertical weight, horizontal weight is increased. It also adds to the complexity and expense of the machine.